tances, as supposed
constituted by a precise and real essence which nature regularly imparts
to every individual of that kind, whereby it is made to be of that
species, we cannot be certain of the truth of any affirmation or
negation made of it. For man or gold, taken in this sense, and used
for species of things constituted by real essences, different from the
complex idea in the mind of the speaker, stand for we know not what; and
the extent of these species, with such boundaries, are so unknown and
undetermined, that it is impossible with any certainty to affirm, that
all men are rational, or that all gold is yellow. But where the nominal
essence is kept to, as the boundary of each species, and men extend the
application of any general term no further than to the particular things
in which the complex idea it stands for is to be found, there they are
in no danger to mistake the bounds of each species, nor can be in doubt,
on this account, whether any proposition be true or not. I have chosen
to explain this uncertainty of propositions in this scholastic way, and
have made use of the terms of ESSENCES, and SPECIES, on purpose to show
the absurdity and inconvenience there is to think of them as of any
other sort of realities, than barely abstract ideas with names to them.
To suppose that the species of things are anything but the sorting of
them under general names, according as they agree to several abstract
ideas of which we make those names signs, is to confound truth, and
introduce uncertainty into all general propositions that can be made
about them. Though therefore these things might, to people not possessed
with scholastic learning, be treated of in a better and clearer way
yet those wrong notions of essences or species having got root in most
people's minds who have received any tincture from the learning which
has prevailed in this part of the world, are to be discovered and
removed, to make way for that use of words which should convey certainty
with it.

5. This more particularly concerns Substances.

The names of substances, then, whenever made to stand for species which
are supposed to be constituted by real essences which we know not, are
not capable to convey certainty to the understanding. Of the truth
general propositions made up of such terms we cannot be sure. [The
reason whereof is plain: for how can we be sure that this or that
quality is in gold, when we know not what is or is not gold? Since